The present invention relates to a radio frequency coil front end interface system for magnetic resonance scanners. The invention finds particular application in conjunction with an intelligent detection and recognition system for identifying and diagnostic testing of a radio frequency coil. The invention also finds application in conjunction with the cable connection system for interconnecting the radio frequency coil and the interface system.
Magnetic resonance imagers commonly include a bore dimensioned to receive a patient to be imaged. The bore is surrounded by a toroidal superconducting magnet for generating a temporally constant magnetic field axially through the bore. Whole body radio frequency and gradient coils typically surround the bore. A patient couch supports and transports the patient into and out of the bore. More specifically, the patient couch is commonly height adjustable. The patient supporting surface is retractable from the bore for positioning the patient thereon and extendible into the bore.
When doing localized scans such as head or heart scans, a localized coil is commonly positioned in the bore with the patient. Cables, typically coaxial cables, are connected between the insertable coil and a radio frequency transmitter and receiver.
U.S. Pat. No. 4,972,852 of Koob discloses a head coil with an 8-pin connector. A selected one or a selected pattern of the pins are connected to ground to provide an 8-binary bit identification of the insertable coil. A digital circuit reads which pins are and are not shorted to ground as 1's and 0's and uses digital logic gates to indicate to the computer the type of coil installed. One disadvantage of this system is that it is very complex to manage a multiple analog conductor cable because it is large and prone to pick up stray radio frequency signals. Moreover, when one of the wires or contacts fails, an incorrect indication of the nature of the installed coil is provided to the computer. This erroneous indication of the installed coil could cause an imaging sequence to be initiated which could injure the patient or cause damage to the magnetic resonance equipment.
U.S. Pat. No. 5,144,244 of Kess illustrates a decoupling system for radio frequency antennas. A DC current is applied to both the transmit and receive coils which are wired in series such that RF power will only be transmitted into the patient if pin diode couplers in the receive coil are shorted (when the receive coil is decoupled) or in the normal operating condition. If the receive coil pin diode is open indicating a failure, the transmit coil exhibits a high reflected RF power reflecting RF signal from the transmitter back to the transmitter rather than into the patient. One drawback of this system is that it provides no direct indication of coil failure. The large reflected power may cause the RF amplifier to shut down in one of its fault modes. If the RF transmitter does not shut down, there is no feedback to the remainder of the system that a magnetic resonance imaging sequence is not running normally.
In a Philips T5/S15 magnetic resonance system, a constant voltage source is applied to a pin of a non-RF signal conductor on a surface coil. A set of analog comparators compare this voltage to reference voltages to determine the normal operating mode of the coil, i.e, whether the coil is a receive only coil, a transmit and receive coil, or a multi-nuclear coil. In response to this comparison, DC signal is applied to the coil to provide appropriate biasing for the identified mode of operation. One drawback to this type of system is that it complicates the connector because extra pins are needed for identifying the coil type. The system has no check of the level of current in the coil and could indicate an incorrect type of coil. Further, there is no check that the coil is, in fact, functioning in the identified mode.
The present invention contemplates a new and improved front end interface system which overcomes the above-referenced problems and others.